1. Field of the Invention
The present invention relates to an LED display apparatus. More particularly, the present invention relates to an LED display apparatus that is adapted to be installed on a place where it can be directly touched by a hand of a user.
2. Description of the Related Art
There have been widely used display apparatus in which a plurality of light-emitting portions using LEDs (light-emitting diodes) as display devices are arranged in the form of segments or a matrix to constitute a display element, as well as display apparatus in which a plurality of display modules each being formed by matrices of light-emitting portions are arranged like tiles.
Most of these conventional display apparatus (referred to as xe2x80x9cLED display devicesxe2x80x9d in this specification) have large pixel pitches (pitches among the individual light-emitting portions) and, hence, offer low resolution.
Therefore, the LED display devices that display images upon receiving video signals must be watched from a visual regognition distance and are, hence, generally installed outdoors, such as on a wall of a building where they cannot be directly touched by human hand.
Recently, however, there has been proposed an LED display device having a small pixel pitch so that it can be watched from a short visual recognition distance, suggesting increasing chances for installing the LED display devices for displaying images on a place where they can be directly touched by human hand in the future.
When the LED display device is installed on a place where it can be directly touched by human hand as described above, there arises a probability that, when the human hand approaches the display surface, an electrostatic discharge may take place between the electrically charged human body and the LED display device that is grounded, and an electric current may flow into the light-emitting portions and the driving ICs due to the electrostatic discharge, resulting in a malfunctioning or breakage of the light-emitting portions and the driving ICs. Therefore, the LED display device installed on such a place requires a countermeasure against damage caused by static electricity.
As one of the countermeasures, it has been attempted as shown, for example, in FIG. 5, to attach louvers 11 which are protrusions extending in a Z-direction in FIG. 5 among the rows of light-emitting portions L arranged like a matrix on the display surface of the LED display device.
By arranging the louvers 11, positions close to the light-emitting portions L inside of the louvers 11 are not accessible by human hand; i.e., a predetermined distance equal to a difference between the height of the louvers 11 and the height of the light-emitting portions L is maintained between the human hand and the light-emitting portions L.
Due to this distance, it is difficult that the current of electric discharge flows into the light-emitting portions or into the driving ICs despite of the occurrence of an electrostatic discharge, lowering the probability of malfunction or breakage in the light-emitting portions and the driving ICs.
According to another countermeasure as shown in, for example, FIG. 6, the whole display surface of the LED display device is covered with a transparent protection film 12. By covering the display surface with the protection film 12, a predetermined distance is also maintained between the human hand and the light-emitting portions L. Even when an electrostatic discharge occurs, therefore, the current of electric discharge does not flow to the light-emitting portions and the driving ICs.
There has been proposed a further LED display device in which the light-emitting portions are mounted on a base plate, such as circuit board, with their lead portions (connection terminals) being exposed. FIG. 7 illustrates an example of the light-emitting portions of this structure, wherein LED lamps 31 of the shape of a bullet are mounted on the LED base plate 32 with the lead portions 31a being exposed. In the LED display device having such LED lamps 31, a current due to the electrostatic discharge flows from the lead portions 31a into the LED chips in the LED lamps 31 and into the driving ICs on the LED base plate 32, causing a malfunction or a breakage in the LED lamps 31 and in the driving ICs.
In this LED display device, therefore, it has heretofore been attempted, as shown in FIG. 7, to drip a thermosetting silicone resin (or an urethane resin, etc.) 34 from the upper side of the LED base plate 32 contained in a cell case 33 to prevent the leakage of the resin, thereby to seal the lead portions 31a with the silicone resin 34, as a countermeasure for preventing damage due to static electricity.
By sealing the lead portions 31a with the silicone resin 34 as described above, the current caused by the electrostatic discharge does not flow into the lead portions 31a, lowering the probability of malfunction or breakage in the LED lamps 31 and in the driving ICs.
When the protuberances such as louvers protruding forward beyond the light-emitting portions are attached on the display surface as shown in FIG. 5, however, the light-emitting portions are shielded by the protrusions and cannot be seen when the display surface is watched from an upper inclined direction or from a lower inclined direction. Thus, the protuberances such as louvers narrow the visible angle and worsen the visual recognition particularly when the LED device is installed at a close distance so that it can be directly touched by human hand.
Further, when the display surface is covered with the protection film as shown in FIG. 6, the external light (sunlight when the display device is installed outdoors, or light of illumination when the display device is installed indoors) is reflected by the protection film, whereby the surrounding scenery is reflected on the display surface and light from the light-emitting portions is partly absorbed by the protection film lowering the brightness. In this case, too, therefore, the visual recognition to the LED display device is worsened.
Thus, the countermeasures employed in the examples of FIGS. 5 and 6 are accompanied by such an inconvenience as worsening the visual recognition to LED display device.
Besides, the protection film employed in the example of FIG. 6 is generally expensive driving up the cost of producing the LED display device of a large screen.
Moreover, even when a predetermined distance is maintained between the human hand and the light-emitting portions by attaching the protrusions such as louvers or by covering the display surface with the protection film as done in FIGS. 5 and 6, the current due to electrostatic discharge often flows into the light-emitting portions and driving ICs over the distance when the potential difference is great between the human body and the LED display device.
Thus, the conventional countermeasures are not capable of reliably preventing damage due to static electricity.
In the case of sealing the lead portions of the LED lamps by potting as shown in FIG. 7, large machining cost and material cost are required for potting, driving up the cost of production.
Further, when the lead portions are sealed with the silicone resin, it becomes difficult to remove the light-emitting portions from the LED base plate. Therefore, in case that some light-emitting portions are found defective in the maintenance after the production, the whole base plate including the light-emitting portions (the whole cell case 33 containing the LED base plate 32 in the example of FIG. 7) must be replaced, resulting in an increase of the cost.
It is an object of the present invention to provide an LED display device which is capable of preventing damage caused by static electricity and of reliably preventing damage caused by static electricity without worsening the visual recognition.
The LED display device of the present invention comprises:
at least one panel having LEDs arranged in the form of a matrix on a display surface; and
an electrically conductive member surrounding the light-emitting portions of said LEDs of said panel.
In this LED display device, therefore, when the hand of a man who arranges it approaches the display surface, the electric current caused by the electrostatic discharge flows into the electrically conductive member surrounding the light-emitting portions. Therefore, the current caused by the electrostatic discharge flows little into the light-emitting portions and into the driving ICs, and it achieves lower probability of malfunctioning or breakage in the light-emitting portions and in the driving ICs.
More preferably, a height of the electrically conductive member is nearly equal to, or not higher than, the height of the light-emitting portions of the LEDs in a direction perpendicular to said display surface.
The electrically conductive member is not greatly protruding forward beyond the position nearly equal to, or smaller than, the height of the light-emitting portions in a direction perpendicular to the display surface, i.e., is not greatly protruding forward beyond the light-emitting portions. The light-emitting portions are arranged at positions where they can be seen without being interrupted by the electrically conductive member even when they are watched from an upper inclined direction or from a lower inclined direction of the display surface. Therefore, the viewing angle is not narrowed unlike when protrusions such as louvers are attached.
Further, since the display surface is not covered with the protection film, the external light is not reflected, the surrounding scenery is not reflected on the display surface, light from the light-emitting portions are not absorbed and, hence, the brightness does not decrease. Thus, damage caused by static electricity is prevented without worsening the visual recognition.
Arranging the electrically conductive member requires less cost than covering the display surface with the protection film, and makes it possible to lower the cost.
In the LED display apparatus having the electrically conductive member arranged therein, it is more desired to ground the electrically conductive member.
Thus, all the currents due to the electrostatic discharge flow into ground from the electrically conductive member. Even when the potential difference is great between the human body and the LED display apparatus, therefore, the current due to the electrostatic discharge does not flow into the light-emitting portions or to the driving ICs, making it possible to reliably prevent damage caused by static electricity.
It is further desired that the electrically conductive member is formed by mounting, on the display surface, an electrically conductive plate having holes perforated at positions corresponding to the positions of the light-emitting portions on the display surface.
The electrically conductive plate can be easily arranged by being mounted on the display surface of the panel.
It is further desired to wire the LEDs on the base plate and to arrange an electrically nonconductive plate between the base plate and the electrically conductive member. This makes it possible to reliably insulate the LEDs, the base plate and the electrically conductive member.
It is further desired to make the display surface of the panel in black color. This easily absorbs light scattered around the light-emitting portions irrespective of the presence of the electrically conductive member, and heightens the contrast of image.
Next, when the LEDs are mounted on the base plate with their lead portions being exposed like in the example of FIG. 7, it is desired to arrange an electrically conductive member to surround the light-emitting portions on the display surface of the LED display apparatus at a position higher than the height of the lead portions in a direction perpendicular to the display surface.
In this LED display apparatus, the electrically conductive member is arranged at a position (protruded forward beyond the lead portions) higher than the height of the lead portions in a direction perpendicular to the display surface. When the human hand approaches the display surface, therefore, the current due to the electrostatic discharge flows into the electrically conductive member. Accordingly, the current due to the electrostatic discharge flows little into the lead portions, lowering the probability of malfunctioning or breakage in the light-emitting portions and in the driving ICs.
The electrically conductive member in the direction perpendicular to the display surface has a height larger than that of the lead portions but is nearly equal to, or smaller than, the height at the ends of the light-emitting portions (i.e., without protruding forward beyond the light-emitting portions). Therefore, the light-emitting portions can be seen without being interrupted by the electrically conductive member even when they are watched from an upper inclined direction or from a lower inclined direction of the display surface. Thus, damage caused by static electricity is prevented without worsening the visual recognition.
Arranging the electrically conductive member requires less cost than sealing the lead portions by potting as is done in the prior art, and makes it possible to lower the cost.
In the LED display apparatus having the electrically conductive member arranged therein, it is more desired to ground the electrically conductive member.
Thus, all the currents due to the electrostatic discharge flow into ground from the electrically conductive member. Even when the potential difference is great between the human body and the LED display apparatus, therefore, the current due to the electrostatic discharge does not flow into the lead portions, making it possible to reliably prevent damage caused by static electricity.
It is further desired that the electrically conductive member is formed by using an electrically conductive plate having holes perforated at positions corresponding to the positions of the light-emitting portions on the display surface.
By using the above electrically conductive plate, it is allowed to easily arrange an electrically conductive member not protruded forward beyond the lead portions but not protruded forward beyond the ends of the light-emitting portions.
Even in case that some light-emitting portions become defective after the production, the electrically conductive plate is taken out to easily remove only those defective light-emitting portions from the LED base plate to repair or replace them. Therefore, even the maintenance requires a decreased cost compared with when the lead portions are sealed by potting as done in the related art.